On the preparation and NMR spectroscopic characterization of potassium aluminium tetrahydride KAlH4

Potassium aluminium tetrahydride KAlH4 of high phase purity (space group Pnma (62)) was synthesized via a mechanochemical route. The thus obtained material was studied by 27Al and 39K MAS NMR spectroscopy. For both nuclei precise data for the isotropic chemical shift and the quadrupole coupling at T=295 K were derived (27Al: delta_iso=(107.6±0.2) ppm, C_Q = (1.29±0.02) MHz and eta = 0.64±0.02; 39K: delta_iso=(6.1±0.2) ppm, C_Q = (0.562±0.005) MHz and eta = 0.74±0.02). The straightforward NMR spectroscopic approach applied here should also work for other complex aluminium hydrides and for many other materials containing half-integer nuclei experiencing small to medium-sized quadrupole couplings.